1. Field of the Invention
The present invention relates to a high voltage terminal for connecting an ignition cable to a terminal of approximately columnar shape such as an end terminal of an ignition plug.
2. Description of Background Information
Conventionally, the structure of the connecting part between the ignition cable and the ignition plug has been constituted as shown in FIG. 10.
According to this structure of the connecting part, an ignition plug P is fitted to the engine body E such that the insulator part Pg at the top of the ignition plug P projects upwardly. At the upper part of the insulator part Pg, a ball-topped, generally columnar end terminal Pt projects for receiving a secondary high voltage from the ignition coil. Also, a rubber boot 100 is provided to accommodate a high voltage terminal 110 at the end of the ignition cable K. The rubber boot 100 is engaged with the insulator part Pg of the ignition plug P, and inside the rubber boot the high voltage terminal 110 and the end terminal Pt are held in an electrically connected state. Furthermore, the rubber boot 100 is covered with a metal heat shielding member 105, thereby preventing thermal degradation of the rubber boot 100 by shielding radiating heat from a heat generation source such as exhaust pipe.
In the construction shown in FIG. 11, a high voltage terminal 110 is formed by continuous connection on a straight line, through a connecting part 116, of a tubular terminal 114 on one end of a channel-shaped, press-fit clamping part 112 having a projection 111 at the tip of both sides. Also, a portion of the continuous connecting part 116 and the bottom part of the terminal 114 are cut and deformed upwardly to form a contact piece 117 projecting between the press-fit clamping part 112 and the tubular terminal 114. When the end of the ignition cable K is accommodated in the press-fit clamping part 112 and its end is press-fitted to the contact piece 117, the press-fit clamping part 112 is deformed inwardly to press-fit the projection 111 in a manner to bite into the outer peripheral part of the ignition cable K, such that the high voltage terminal 110 is fixed to the ignition cable K end.
A generally C-shaped elastic C-ring member 118 is clipped onto the above terminal 114. This C-ring member 118 is formed in a manner to be fitted onto the terminal 114, as shown in FIG. 12, and on both sides of its inner peripheral surface are formed a pair of projections 119 which project inwardly. On the other hand, on the outer peripheries of both sides of the terminal 114 are formed a pair of stopping holes 115 within which the projections 119 may be engaged. By applying the C-ring member 118 to the terminal 114 in a manner to engage each projection 119 within each stopping hole 115, the C-ring member 118 is fixed to the high voltage terminal 110.
According to this construction of the high voltage terminal 110, by inserting the end terminal Pt of the ignition plug P into engagement with the terminal 114, the high voltage terminal 110 and the end terminal Pt of the ignition plug P are electrically connected.
In order to assemble the structure of the connecting part between the ignition cable K and the ignition plug P using the high voltage terminal 110 of such construction, when the rubber boot 100 is engaged in the insulator Pg of the ignition plug P, the end terminal Pt must be inserted deep within the high voltage terminal 110 for the connection to be sufficiently attained. However, if, for example, under the condition where the rubber boot 100 is engaged with the insulator Pg, and insertion of the end terminal Pt into the terminal 114 is shallow and their engagement is insufficient, there is a risk of accidental firing of the ignition plug or stoppage of engine due to a faulty electrical connection between the high voltage terminal 110 and the end terminal Pt. Even if the insertion of the end terminal Pt into the terminal 114 is not shallow, if the relative positions between the end terminal Pt and the terminal 114 are inadequate due to displacement or the like, the high voltage terminal 110 and the end terminal Pt may be abraded or vibrated by engine vibration and the like to cause unsatisfactory electric connection between the high voltage terminal 110 and the end terminal Pt, thereby providing a risk of accidental firing of the ignition plug or stoppage of engine.
In order to prevent the above drawbacks, it is necessary to provide improved dimensional precision of parts such as the rubber boot 100, the high voltage terminal 110, and the like, and improvement in precision of the assembly position of these parts, especially of the high voltage terminal 110 into the rubber boot 100, thereby inviting the total increase in cost of this structure and loss of assembly efficiency.
Accordingly, in conventional constructions to ensure electrical connection between the high voltage terminal 110 and the end terminal Pt, there are devices using spring members, as shown in FIG. 13 or FIG. 14.
In a high voltage terminal 140 shown in FIG. 13, a stopper 144 projecting inwardly on a peripheral wall of the generally tubular shaped terminal part 142 is formed over the entire periphery of the terminal part. On the other hand, the spring member 146 is formed at one end to have a portion with a larger diameter than the intermediate portion of the spring. The high voltage terminal 140 is configured so that, by pushing the spring member 146 into the terminal part 142, the enlarged diameter portion 146 a rides over the stopper 144 and is disposed on the opposite side of the stopper 144, so that the spring member 146 is fixedly received within the terminal part 142.
When an end terminal Pt is inserted in the terminal 142 of the high voltage terminal 140, the spring member 146 is compressed and forced to be pressed to the end terminal Pt, thereby allowing the electrical connection between the high voltage terminal 130 and the end terminal Pt to be made with greater assurance.
Japanese Utility Model Laid-open Publication HEI 5-66891 and U.S. Pat. No. 5,340,323 (which corresponds to the Japanese document) are noted as showing techniques related to the high voltage terminal of FIG. 13.
In a high voltage terminal 150 shown in FIG. 14, an insertion port 154 is formed on one side of the peripheral wall of the generally tubular terminal part 152. On the other hand, the C-ring member 158, which is clipped over the terminal 152 as shown in FIG. 14 and FIG. 15, is formed with a tongue piece 159 which can be inserted into the terminal part 152 through the insertion port 154. According to this construction, by clipping the C-ring member 158 over the terminal part 152 and inserting the tongue piece 159 into the terminal part 152 from the insertion port 154, the tongue piece 159 is inserted into a gap between the pitch of the spring member 156 to hold the end of the spring member 156 at a predetermined position in the terminal part 152.
With this high voltage terminal 150, in the same manner as in the situation of FIG. 13, when an end terminal Pt is inserted in the terminal part 152, the spring member 156 is compressed and forced in a manner to be pressed to the end terminal Pt, thereby allowing a more positive electric connection between the high voltage terminal 150 and the end terminal Pt.
Japanese Utility Model Laid-open Publication HE16-80295 and U.S. Pat. No. 5,421,736 (which corresponds to the Japanese document) are noted as showing techniques related to the high voltage terminal of FIG. 14.
However, in the high voltage terminal 140 shown in FIG. 14, the other end of the spring member 145 projects outward from the opening of the terminal 142 in the non-compressed state, so that, upon inserting the end terminal Pt of the ignition plug P into the terminal 142, the spring member 146 may be caught by the opening of the terminal 142 or the spring member 146 may be dislocated sideways.
In this case, it is still insufficient to configure the inside of terminal 142 to fully accommodate the spring member 146 so as to prevent the other end of the spring member 146 from projecting outside the terminal 142. This is because, in such a case, the spring member 146 must be pushed deep into the terminal 142 while being installed so that the large diameter part 146a of the spring member 146 runs over the stopper 144 of the terminal 142, and a specific jig is required that can be inserted into the terminal 142, with the result that the inserting work itself is a problem.
In the high voltage terminal 150 shown in FIG. 14, because the construction is configured to insert the tongue piece 159 of the C-ring member 158 into the gap between the pitches of the spring member 156, there may be times where the tongue piece 159 is inserted into an improper position in the gap between the pitches of the spring member 156, because the spring member 156 is fitted into the terminal 152 in an inclined position, or where the tongue piece 159 is not pressed into a portion of the pitch gap of the spring member 156, i.e., it is pressed into the spring member 156 itself which may result in deformation of the spring member 156. Consequently, the spring member 156 may be destroyed by vehicle vibration.
Accordingly, the present invention has been made to solve the problems described above, and an object is to provide a high voltage terminal for an ignition cable which makes it possible to easily and more accurately position a spring member within the terminal section in order to more positively provide electrical connection of an ignition plug with a generally columnar terminal, such as an end terminal.